Hydrophobic silica microparticles and composition for electrophotographic toner

Abstract

Provided are silica microparticles having a fine primary particle size suitable for an external toner additive, the microparticles including no bulky agglomerated particles responsible for a decrease in dispersibility into toner and fluidity of toner. The microparticles are capable of preventing detachment from toner, and are superior in effects of imparting uniform dispersibility and fluidity, thereby preventing a white point on printed images from occurring. The silica microparticles are characterized in that the silica microparticles are produced using hexamethyl disilazane or organo-polysiloxane by carrying out hydrophobization of hydrophilic silica microparticles having an average primary particle size of from 20 to 100 nm produced by a gas phase method, and that a ratio of agglomerated particles having a particle size of 1.5 μm or more is less than a predetermined value by determining using laser diffractometry by a volume-based particle size measurement of the particle.

1 . Hydrophobic silica microparticles produced by hydrophobization of hydrophilic silica microparticles using hexamethyl disilazane, the hydrophilic silica microparticles having an average primary particle size of 20 to 100 nm produced by a gas phase method, wherein a ratio of agglomerated particles having a particle size of 1.5 μm or more to all hydrophobic silica microparticles is less than 8%, the particle size being determined by a volume-based particle size measurement using laser diffractometry. 
     
     
         2 . The hydrophobic silica microparticles according to  claim 1 , wherein an average primary particle size of the hydrophilic silica microparticles is 50 nm or less. 
     
     
         3 . The hydrophobic silica microparticles according to  claim 1 , wherein a hydrophobicity factor is 95% or more. 
     
     
         4 . The hydrophobic silica microparticles according to  claim 1 , wherein the hydrophobic silica microparticles are silica microparticles used for an external toner additive. 
     
     
         5 . Composition for electrophotographic toner, comprising hydrophobic silica microparticles according to  claim 1 , wherein the microparticles are externally added to the composition. 
     
     
         6 . Hydrophobic silica microparticles produced by hydrophobization of hydrophilic silica microparticles using organo-polysiloxane, the hydrophilic silica microparticles having an average primary particle size of 20 to 100 nm produced by a gas phase method, wherein a ratio of agglomerated particles having a particle size of 1.5 μm or more to all hydrophobic silica microparticles is less than 12%, the particle size being determined by a volume-based particle size measurement using laser diffractometry, the polysiloxane represented by general formula (I): 
       
         
           
           
               
               
           
         
       
       wherein R and R′ represent hydrogen, alkyl having a carbon number of 1 to 3, or aryl;
 R″ represents alkyl having a carbon number of 1 to 3 or hydroxyl, or represents a bond which forms cyclic siloxane by representing one oxygen atom together with both R″s; 
 n and m each represent an integer of 0 or more where the total of n and m is 2 or more; 
 R′ is different from R, and R′ and R″, or R and R″ may be the same or different; and 
 five Rs refer to the same R, and two R″s may be the same or different. 
 
     
     
         7 . The hydrophobic silica microparticles according to  claim 6 , wherein an average primary particle size of the hydrophilic silica microparticles is 50 nm or less. 
     
     
         8 . The hydrophobic silica microparticles according to  claim 6 , wherein a hydrophobicity factor is 97% or more. 
     
     
         9 . The hydrophobic silica microparticles according to  claim 6 , wherein the hydrophobic silica microparticles are silica microparticles used for an external toner additive. 
     
     
         10 . Composition for electrophotographic toner, comprising hydrophobic silica microparticles according to  claim 6 , wherein the microparticles are externally added to the composition.